Log warning message when deprecated network name 'tor' is used (e.g. option onlynet=tor)

Summary: This is a backport of core PR13532

Test Plan:

make check

The function is unit tested

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D2823